Automatic meter reading (AMR) systems are generally known in the art. Utility companies, for example, use AMR systems to read and monitor customer meters remotely, typically using radio frequency (RF) communications. AMR systems are favored by utility companies and other users because the systems increase the efficiency and accuracy of collecting readings and managing customer billing. For example, using an AMR system for the monthly reading of residential gas, electric, or water meters eliminates the need for a utility employee to physically enter each residence or business where a meter is located to transcribe a meter reading by hand.
There are several different ways in which current AMR systems are configured. In a fixed network, endpoint devices at meter locations communicate with readers that collect readings and data using RF. Here and throughout this document, the term “endpoint device” will be used to generally refer to the meter and meter interface unit that communicates with the reader as a single device, although in various embodiments the meter and meter interface unit may be distinct devices in electrical communication but not physical proximity with each other. There may be multiple fixed intermediate readers located throughout a larger geographic area on utility poles, for example, with each endpoint device associated with a particular reader and each reader in turn communicating with a central system. Other fixed systems utilize only one central reader with which all endpoint devices communicate. In a mobile environment, a handheld or otherwise mobile reader with RF communication capabilities is used to collect data from endpoint devices as it is moved from place to place.
U.S. Pat. No. 5,914,673, for example, relates to an AMR system of the type used for reading utility meters by using a fixed RF network. The system is a network comprised of multiple cells, with each cell containing a single data concentrator unit and a typically large number of meter interface units. In operation, each meter interface unit is assigned a unique time displacement number and responds to a meter reading request from a data concentrator unit based upon its time displacement number.
A concern regarding both fixed networks and mobile environments is endpoint battery consumption. Each endpoint device is typically equipped with a battery-powered meter interface unit that communicates with the reader. To contribute to the overall system goal of increased efficiency and accuracy of meter reading, it is desirable to prolong the meter interface battery life to reduce time and expense maintaining and servicing the batteries in the meter interfaces. Since using a battery with a larger capacity is generally not a viable option due to cost and space considerations, the preferred method with which to increase battery life is to reduce battery consumption by the meter interface. This goal may be accomplished in part by operating the meter interface in a “sleep” or reduced power mode when communication with the reader is not expected or required.
U.S. Pat. No. 5,726,646 is directed to a method and apparatus for activating and accessing remote meter interface devices. A meter reading device initiates communication with a meter interface unit by transmitting a request on a communication channel. The meter interface unit is operable between an active and inactive state to reduce power consumption and is periodically activated to monitor a communication channel for channel activity. The request from the meter reading device includes a unit identifier, and the meter interface unit is activated at a particular time period and detects communication activity on the communication channel originating from the meter reading device.
Other methods of reducing battery consumption have also been attempted in which the endpoint devices respond only to signals above a particular threshold or only to signals that include some type of system identifier. These methods help to reduce power consumption by limiting the signals that a particular endpoint device will respond to.
U.S. Pat. No. 5,684,472 is directed to a method and apparatus for remotely accessing meter status information in a meter reading system. Communications between battery powered meter interface units and a meter reading device occur at a first data rate, while communications between the externally powered meter interface units and the meter reading device occur at a second data rate different than the first data rate. Communications between battery powered meter interface units and externally powered meter interface units occur at different rates so that more frequent communication with externally powered meter interface units does not result in extended receiver on-time for the battery powered meter interface units.
Other systems use analog squelch techniques based on received signal strength indicators to preserve battery power consumption. These methods, however, are prone to falsing because of interference from other sources. It is also difficult to set the received signal strength threshold level accurately in systems having many endpoint devices because the environmental conditions vary at different locations and change over time and temperature, which cannot be easily or automatically compensated for by the system. This leads to the setting of either an artificially high threshold value, which will miss some endpoint queries and lower system quality of service due to the receiver threshold being above the noise floor, or the setting of a low threshold, which will deplete the battery due to excessive falsing.
Systems in which the endpoint devices look for a specific system identifier in the demodulated data require that the endpoint receiver be brought up long enough to recover data and retrieve bit and frame synchronization. This depletes the battery in a system in which the endpoint receiver must repeat this process every few seconds.
There is, therefore, a need in the industry for a system and method of operating AMR systems that conserves battery life while not sacrificing communication capabilities or performance.